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ScienceDaily (Aug. 7, 2012) — If you’re looking for information on the evolution and function of jaws, University of Notre Dame researcher Matt Ravosa is your man.

Matt Ravosa with a llama. (Credit: Image courtesy of University of Notre Dame)

His integrative research program investigates major adaptive and morphological transformations in the mammalian musculoskeletal system during development and across higher-level groups. In mammals, the greater diversification and increasingly central role of the chewing complex in food procurement and processing has drawn considerable attention to the biomechanics and evolution of this system. Being among the most highly mineralized, and thus well-preserved, tissues in the body, craniodental remains have long been used to offer novel insights into the behavior and affinities of extinct organisms.

Ravosa feels that the study of mandibular symphysis, which is the midline joint between the left and right lower jaws, is one of the most interesting and complex articulations in the bodies of mammals. This is due to the remarkable evolutionary and postnatal variation in the degree of fusion, or the amount of hard versus soft tissue, in this joint. For instance, humans, apes and monkeys all have a bony symphysis, which differs from the condition observed in most other living and fossil primates.

In two papers about adaptive and non-adaptive influences on mandibular evolution with his postdoctoral fellow Jeremiah Scott, Ravosa and his colleagues present analyses based on more than 300 species and 2,900 individual mandibles from highly diverse mammal groups where the feeding behavior of living species is well-documented.

Ravosa is particularly interested in determining if there is a relationship between the properties of food being consumed and the degree of fusion of the jaw. His recent paper in the Journal of Evolutionary Biology is the most broad-based examination to date relating dietary properties of mammals to the degree of fusion. His research reveals that in the case of marsupials, carnivorans and strepsirrhine primates that eat harder, tougher and bigger foods have a lesser degree of fusion. By contrast, animals that consume softer, smaller foods do not have as great a degree of fusion. This supports biomechanical arguments that fusion strengthens the symphyseal joint during postcanine chewing and biting.

In another paper appearing in the journal Evolution, Ravosa reports that in some bat lineages, the fusing of the jaw can be evolutionarily constrained as its morphology does not vary as a function of dietary products. Such evidence about limits on musculoskeletal variation is typically rare in mammals, with these findings having important implications regarding the evolution of the feeding apparatus in humans and other anthropoids. Though dietarily diverse, all members of this primate group exhibit a fused symphysis that also does not vary with diet.

Ravosa notes that similar analysis of other species would further help our understanding of the evolution and development of the mammalian skull, which includes his lab’s ongoing anatomical, imaging, cellular, molecular and engineering approaches to determinants of jaw-joint formation, aging and pathology.

ScienceDaily (Aug. 7, 2012) — Dividing tasks among different individuals is a more efficient way to get things done, whether you are an ant, a honeybee or a human.

(Credit: Adele Conover)

A new study by researchers at Michigan State University’s BEACON Center for the Study of Evolution in Action suggests that this efficiency may also explain a key transition in evolutionary history, from single-celled to multi-celled organisms.

The results, which can be found in the current issue of the Proceedings of the National Academy of Sciences, demonstrate that the cost of switching between different tasks gives rise to the evolution of division of labor in digital organisms. In human economies, these costs could be the mental shift or the travel time required to change from activity to another.

Using the digital evolution platform Avida, self-replicating computer programs, a the team imposed a time cost on the organisms that had to perform different computational tasks to get rewards, said Heather Goldsby, who led the study and is now a postdoctoral researcher at the University of Washington.

“More complex tasks received more rewards,” she said. “They evolved to perform these more efficiently by using the results of simpler tasks solved by neighboring organisms and sent to them in messages.”

In this way, the organisms were breaking the tasks down into smaller computational problems and dividing them up among each other.

The division of labor did not come about by bringing together individuals with different abilities — each member of a community was genetically identical, in the same way that all of the cells in a human body contain the same genetic material. Instead, the organisms had to have flexible behavior and a communication system that allowed them to coordinate tasks.

The most surprising result was that the organisms evolved to become dependent on each other.

“The organisms started expecting each other to be there, and we tested them in isolation, they could no longer make copies of themselves,” said Charles Ofria, MSU associate professor of computer science and engineering.

Ben Kerr at the University of Washington and Ann Dornhaus with the University of Arizona contributed to this study. The research was funded by the National Science Foundation.

Michigan State University (2012, August 7). Division of labor offers insight into the evolution of multicellular life. ScienceDaily. Retrieved August 9, 2012, from http://www.sciencedaily.com­ /releases/2012/08/120807132211.htm

ScienceDaily (Aug. 6, 2012) — The American paddlefish — known for its bizarre, protruding snout and eggs harvested for caviar — duplicated its entire genome about 42 million years ago, according to a new study published in the journal Genome Biology and Evolution. This finding may add a new twist to the way scientists study how fins evolved into limbs since the paddlefish is often used as a proxy for a more representative ancestor shared by humans and fishes.

A juvenile paddlefish, just under three inches long at two months old. Fully grown American paddlefish can reach five feet (1.5 m) in length and have a protruding snout or “rostrum.” A new study by researchers at San Francisco State University finds that the American paddlefish underwent a genome duplication 42 million years ago. (Credit: Diane Fenster/ San Francisco State University)

“We found that paddlefish have had their own genome duplication,” said Karen Crow, assistant professor of biology at San Francisco State University. “This creates extra genetic material that adds complexity to comparative studies. It may change the way we interpret studies on limb development.”

In order to study how human limbs develop, scientists compare the limb-building genes found in mice with fin-building genes found in fishes. Previous research on paddlefish has suggested that fishes possessed the genetic toolkit required to grow limbs long before the evolution of the four-limbed creatures (tetrapods) that developed into reptiles, birds, amphibians and mammals.

In the last decade, paddlefish have become a useful benchmark in evolutionary studies because their position on the evolutionary tree makes them a reasonably good proxy for the ancestor of the bony fishes that evolved into tetrapods such as humans. However, the fact that paddlefish underwent a genome duplication could complicate what its genes tell us about the fin-to-limb transition, says Crow.

“Our findings suggest that the results of previous studies using paddlefish as a comparative species may need to be re-interpreted,” Crow said.

Whole genome duplications are game-changing events in evolutionary history that give rise to new species or novel features within a species. They occur when a series of unlikely circumstances coincide, resulting in twin copies of every gene. When this happens, one scenario that could take place is that one gene in the pair keeps its designated function while the other is either lost or takes on a new purpose.

“This extra genetic material provides the canvas for evolution to paint with,” said Crow, who studies the evolution of novelty and diversity.

Two milestone genome duplications are believed to have taken place before the evolution of jawed vertebrates. Additional whole genome duplications have also taken place further down the evolutionary tree, in specific lineages or branches, but it is a phenomenon more common in plants than animals.

“Our findings on the paddlefish suggest that whole duplication is not as uncommon in animals as previously thought,” Crow said.

San Francisco State University (2012, August 6). Paddlefish’s doubled genome may question theories on limb evolution. ScienceDaily. Retrieved August 9, 2012, from http://www.sciencedaily.com­ /releases/2012/08/120807101343.htm

ScienceDaily (Aug. 3, 2012) — Just as differences in song can be used to distinguish one bird species from another, the pips and squeaks bats use to find prey can be used to identify different species of bat. Now, for the first time, ecologists have developed a Europe-wide tool capable of identifying bats from their echolocation calls.

The new free online tool — iBatsID — will be a major boost to conserving bats, whose numbers have declined significantly across Europe over the past 50 years. Details are published August 7 in the British Ecological Society’s Journal of Applied Ecology.

Working with an international team of ecologists, lead author and PhD student Charlotte Walters from the Zoological Society of London (ZSL) selected 1,350 calls of 34 different European bat species from EchoBank, a global echolocation library of more than 200,000 bat calls.

The calls were then analysed to find out which characteristics were most useful in distinguishing different bat species. According to Walters: “Lots of different measurements can be taken from an echolocation call, such as its maximum and minimum frequency, how quickly the frequency changes during the call, and how long the call lasts, but we didn’t know which of these measurements are most useful for telling different species’ calls apart.”

The 12 most useful call parameters were then used to train artificial neural networks to produce the new identification tool, iBatsID, which can identify 34 different bat species across the whole of Europe. Most species can be identified correctly more than 80% of the time, although accuracy varies because some species are much harder to identify than others.

“iBatsID can identify 83-98% of calls from pipistrelle species correctly, but some species such as those in the Myotis genus are really hard to tell apart and even with iBatsID we can still only identify 49-81% of Myotis calls correctly,” she explains.

iBatsID should have a major impact on European bat conservation, which until now has been hampered by the absence of a standardised, objective and continent-scale identification tool.

According to Professor Kate Jones, another of the paper’s authors and chair of the Bat Conservation Trust: “Acoustic methods are really useful for surveying and monitoring bats, but without using the same identification methods everywhere, we can’t form reliable conclusions about how bat populations are doing and whether their distributions are changing. Because many bats migrate between different European countries, we need to monitor bats at a European, as well as at country, scale. In iBatsID, we now have a free, online tool that works anywhere in Europe.”

Bat populations have declined significantly across Europe since the middle of the 20th century. As a result, all bats are now protected through the EU Habitats Directive. Bats face many pressures, including loss of roosting sites in trees and buildings; loss of feeding habitats in woodlands, meadows, parks and gardens; falling insect numbers; and habitat fragmentation resulting in the loss of green corridors such as hedges that provide connectivity in the landscape.

As well as providing vital ecosystem services, such as pollinating plants and controlling insect pests, bats are important indicators of biodiversity. “Bats are very sensitive to changes in their environment, so if bat populations are declining, we know that something bad is going on in their environment. Monitoring bats can therefore give us a good idea of what is going on with biodiversity in general,” Walters adds.

ScienceDaily (Aug. 6, 2012) — Hearing generic language to describe a category of people, such as “boys have short hair,” can lead children to endorse a range of other stereotypes about the category, a study by researchers at New York University and Princeton University has found. Their research, which appears in the Proceedings of the National Academy of Sciences (PNAS), also points to more effective methods to reduce stereotyping and prejudice.

The study focused on “social essentialism,” or the belief that certain social categories, such as race or gender, mark fundamentally distinct kinds of people. For instance, social essentialism facilitates the belief that because one girl is bad at math, girls in general will be bad at math. While previous scholarship has shown that essentialist beliefs about social categories, such as gender or race, appear as early as preschool, it has been less clear on the processes that lead to the formation of these beliefs.

This dynamic was the focus of the PNAS study.

Specifically, the researchers tested whether generic language plays a powerful role in shaping the development of social essentialism by guiding children to develop essentialist beliefs about social categories that they would not otherwise view in this manner. In addition, in order to understand how social essentialism is transmitted, they examined whether or not holding essentialist beliefs about a social category leads parents to produce more generic language describing the category when talking to their children.

In the study, the researchers introduced four-year-old children and their parents to a fictional category of people — “Zarpies” — via an illustrated storybook. Each page presented a picture of a single person displaying a unique physical or behavioral property. The characters were diverse with respect to sex, race, and age in order to eliminate the possibility of existing essentialist beliefs influencing the results. For instance, if all of the “Zarpies” were Asian, subjects might apply essentialist beliefs to the group if they generally have essentialist beliefs about race. In the experiment, the adults read the book twice while an experimenter read the book to the children two times.

In two experiments, in which a single line of text described the accompanying pictures, hearing generic language about a novel social category led both preschool-age children and adults to develop essentialist beliefs about the category. For example, subjects in a generic-language condition (“Look at this Zarpie! Zarpies are scared of ladybugs”) were significantly more likely than those in a specific-language condition (“Look at this Zarpie! This Zarpie is scared of ladybugs!”) to express essentialist beliefs — even a few days after the experiment.

A third experiment sought to understand how social essentialism is transmitted — specifically, can parents communicate such beliefs to their children through conversation? To study this, parents were introduced to the category “Zarpies” via a paragraph that led them to hold essentialist beliefs about Zarpies (i.e., by describing Zarpies as a distinct kind of people with many biological and cultural differences from other social groups) or non-essentialist beliefs about Zarpies (i.e., by describing Zarpies as a non-distinct kind of people, with many biological and cultural similarities to other populations).

After reading the introductory paragraph, parents received a picture book containing the illustrations used in studies one and two, with no accompanying text. They were asked to talk through the picture book with their child and describe the people and events depicted, just as they would a picture book at home. No other instructions were provided. The entire parent-child conversation was videotaped and transcribed.

There was no difference in number of utterances or references to the characters between the two conditions. However, a higher percentage of the character references were generic in the essentialist condition compared with the non-essentialist condition. In addition, parents produced more negative evaluations in the essentialist condition than in the non-essentialist condition.

“Taken together, these results showed that generic language is a mechanism by which social essentialist beliefs, as well as tendencies towards stereotyping and prejudice, can be transmitted from parents to children,” said the study’s lead author, Marjorie Rhodes, an assistant professor in NYU’s Department of Psychology.

She added that these results do not show that generic language creates essentialist thought, but, rather, that children’s cognitive biases lead them to assume that some social categories reflect essential differences — and that generic language signals to them to which categories they should apply these beliefs.

“Understanding the mechanisms that underlie the development of social essentialism could provide guidance on how to disrupt these processes, and thus perhaps on how to reduce stereotyping and prejudice,” added co-author Sarah-Jane Leslie, an assistant professor in Princeton’s Department of Philosophy. “We often change the way we speak about a given social group, so grounding these changes in mechanisms shown to influence the formation of essentialist beliefs could lead to more effective efforts to reduce societal prejudice.”

ScienceDaily (Aug. 6, 2012) — Two new studies offer insight into sex chromosome evolution by focusing on papaya, a multimillion dollar crop plant with a sexual problem (as far as growers are concerned) and a complicated past. The findings are described in two papers in the Proceedings of the National Academy of Sciences.

The research reveals that the papaya sex chromosomes have undergone dramatic changes in their short evolutionary histories (they are about 7 million years old; by comparison, human sex chromosomes began their evolution more than 167 million years ago). One of the two studies compares the papaya X chromosome with that of a closely related non-sex chromosome (called an autosome) in a sister species. The other looks at differences between the X and Y chromosomes.

The studies show that the papaya sex chromosomes are increasing in size — mostly through the accumulation of repetitive sequences — while also reorganizing themselves and losing some genes carried over from their days as autosomes. Some of the lost genes are gone without a trace, while other remnants of genes that are no longer functional — called “pseudogenes” — are still present. (The pseudogenes give researchers an opportunity to see evolution in action; they are evidence that the chromosomes are in the process of losing them.)

The papaya Y chromosome also has independently gained some genes from the autosomes, the researchers report.

Gene loss in the Y chromosome is well documented in ancient Y chromosomes, but gene loss in the X chromosome, particularly at this early stage, is unexpected, as is the expansion of the X chromosome, said University of Illinois plant biology professor Ray Ming, who led both studies.

“The pace of gaining repetitive sequences and losing genes is faster in the Y than in the X chromosome, however,” he said.

“This is the first look at an early stage of sex chromosome evolution,” said Andrea Gschwend, who conducted the research with Ming while she was a doctoral student in his lab. “Usually people will focus on the ancient sex chromosomes because they are the most relevant to us,” she said. “So this is the first direct and complete look at a more recently evolved sex chromosome system.”

Analyzing the X chromosome is vital to understanding the evolution of sex, said Ming, an affiliate of the Institute for Genomic Biology at Illinois. The new findings in papaya suggest that the human X chromosome, too, has undergone numerous changes since it first distinguished itself from the autosomes, Ming said. Such changes are not detectable because the ancestral autosomes are no longer available for comparison, he said.

Because the papaya sex chromosomes are young and can be compared to closely related autosomes in a sister species, they offer a view of the early events of both X and Y chromosome evolution, Ming said.

Studying papaya sex chromosomes is a complicated task, however. The papaya has male, female and hermaphrodite sexual types, with two kinds of Y chromosomes (the male Y and the slightly modified, hermaphrodite Yh). Papaya plants may produce combinations of male and female (from the XY system) or hermaphrodite and female (from the XYh system) plants.

This complexity causes problems for papaya growers, Ming said. Hermaphrodites are the most productive of the papaya sexual types and yield the best fruit, but the offspring of hermaphrodites are not all hermaphrodites. To aid growers, Ming and his colleagues aim to develop a “true-breeding” hermaphrodite papaya variety that consistently produces hermaphrodite offspring.

When the researchers compared the X chromosome and the hermaphrodite Yh chromosome, they found that two major sequence inversions in the sex-determining regions of the Yh had taken place. One of these inversions occurred about 7 million years ago, and led the sex chromosomes and the autosomes down very different evolutionary paths, Ming said. The second inversion occurred about 1.9 million years ago and led to further differentiation between them. Each inversion has also undergone numerous sequence rearrangements.

All of the findings are significant and useful, Ming said, but the X chromosome, which is generally overlooked in models of sex chromosome evolution, offered the most surprises.

“These studies are changing our view of sex chromosome evolution, particularly X chromosome evolution,” he said. “We now know that both the X and Y chromosomes are dynamic in the early stages of their evolution, not only the Y chromosome, as previously thought.”

The study team also included researchers from the Hawaii Agriculture Research Center; Texas A&M University; the University of Hawaii, Honolulu; the University of Wisconsin, Madison; the University of Edinburgh; the University of Georgia; and Youngstown State University, Ohio.

University of Illinois at Urbana-Champaign (2012, August 6). Researchers peek at the early evolution of sex chromosomes. ScienceDaily. Retrieved August 9, 2012, from http://www.sciencedaily.com­ /releases/2012/08/120806151242.htm

ScienceDaily (Aug. 6, 2012) — Patterns in nature are in everything from ocean currents to a flower’s petal. Scientists are taking a new look at Earth patterns, studying the biodiversity of yard plants in the U.S. and that of desert mammals in Israel, studying where flowers and bees live on the Tibetan plateau and how willow trees in America’s Midwest make use of water.

Caterpillars feed in a forest in Peru: do insects have an effect on where plants live? (Credit: G. Lamarre)

They’re finding that ecology, the study of relationships between living organisms and their environment, and phylogenetics, research on evolutionary relationships among groups of organisms, are inextricably intertwined.

Results of this tale of two fields are highlighted in a special, August 2012 issue of the journal Ecology, published by the Ecological Society of America (ESA). Most of the results reported are funded by the National Science Foundation (NSF).

The issue will be released at the annual ESA meeting, held this year from August 5-10 in Portland, Ore.

Melding information from ecology and phylogenetics allows scientists to understand why plants and animals are distributed in certain patterns across landscapes, how these species adapt to changing environments across evolutionary time–and where their populations may be faltering.

“To understand the here and now, ecologists need more knowledge of the past,” says Saran Twombly, program director in NSF’s Division of Environmental Biology. “Incorporating evolutionary history and phylogenies into studies of community ecology is revealing complex feedbacks between ecological and evolutionary processes.”

Maureen Kearney, also a program director in NSF’s Division of Environmental Biology adds, “Recent studies have demonstrated that species’ evolutionary histories can have profound effects on the contemporary structure and composition of ecological communities.”

In the face of rapid changes in Earth’s biota, understanding the evolutionary processes that drive patterns of species diversity and coexistence in ecosystems has never been more pressing, write co-editors Jeannine Cavender-Bares of the University of Minnesota, David Ackerly of the University of California at Berkeley and Kenneth Kozak of the University of Minnesota.

“As human domination of our planet accelerates,” says Cavender-Bares, “our best hope for restoring and sustaining the ‘environmental services’ of the biological world is to understand how organisms assemble, persist and coexist in ecosystems across the globe.”

Papers in the volume address subjects such as the vanishingly rare oak savanna ecosystem of U.S. northern tier states, revealing an ancient footprint of history on the savanna as well as how it has fared in a 40-year fire experiment.

Other results cover the influence of ecological and evolutionary factors on hummingbird populations; habitat specialization in willow tree communities; growth strategies in tropical tree lineages and their implications for biodiversity in the Amazon region; and the characteristics of common urban plants.

“The studies in this issue show that knowledge of how organisms evolve reveals new insights into the ecology and persistence of species,” says Cavender-Bares.

Plants in urban yards, for example, are more closely related to each other–and live shorter lives–than do plants in rural areas, found Cavender-Bares and colleagues.

Their study compared plant diversity in private urban yards in the U.S. Midwest with that in the rural NSF Cedar Creek Long-Term Ecological Research site in Minnesota.

Cities are growing faster and faster, with unexpected effects, says Sonja Knapp of the Hemholtz Center for Environmental Research in Germany, lead author of the paper reporting the results.

“Understanding how urban gardening affects biodiversity is increasingly important,” says Cavender-Bares. “Urbanites should consider maintaining yards with a higher number of species.”

In the special issue, researchers also look at topics such as what determines the number of coexisting species in local and regional communities of salamanders. Kenneth Kozak of the University of Minnesota and John Wiens of Stony Brook University report that variation in the amount of time salamanders occupy different climate zones is the primary factor.

Evolution of an herbaceous flower called goldfields, and how that led to the plant’s affinity for certain habitats, is the subject of a paper by David Ackerly, Nancy Emery of Purdue University and colleagues. Emery is the paper’s lead author.

In all, 17 papers combine ecology and phylogenetics to offer new answers to long-standing questions about the patterns and processes of biodiversity on Planet Earth.

National Science Foundation (2012, August 6). Ecology and phylogenetics together offer new views of Earth’s biodiversity. ScienceDaily. Retrieved August 9, 2012, from http://www.sciencedaily.com­ /releases/2012/08/120806130852.htm